4D Visible Human Modeling for Radiation Dosimetry We propose a multidisciplinary research to solve problems associated with patient respiratory motions during radiation therapy by further extending the Visible Human image dataset into the 4th dimension (4D) with motion-simulating capabilities. Radiation therapy is one of the most effective methods of cancer management. In external beam radiation treatment, a lethal radiation dose is delivered through precisely conformed external radiation to the tumor while sparing the adjacent healthy tissues. However, the current paradigm is based on an assumption that both the tumor location and shape are known and remain unchanged during the course of radiation delivery. Such a favorable rigid-body relationship does not exist in anatomical sites such as the thoracic cavity and the abdomen, owing predominantly to respiratory motions. Consequently, the radiation oncologists currently have to use less aggressive treatment strategies with a large dose margin to tolerate potential targeting errors. We propose to develop physics-based, motion-simulating virtual human models that will provide a unique insight into the management of respiratory motion during radiation treatment, thus allowing for more aggressive and effective targeting and radiation delivery. A multidisciplinary research team with collective expertise in radiation dosimetry, biomechanical modeling and clinical radiation oncology is assembled to achieve the following Specific Aims: 1) To combine the 3D adult male anatomical model developed from high-resolution VHP cryosection image data with physics-based tissue deformation models to simulate respiratory motions. 2.)To apply this first physics-based, 4D motion-simulating virtual-human to the study of complex radiation interactions in tissues and dose distribution patterns for various radiation delivery strategies using advanced Monte Carlo simulations, 3).To critically evaluate the degrees to which the more realistic representations of internal organs will improve the planned and delivered treatment doses. 4).To establish an internet-based information-sharing resource on virtual-human motion simulation and radiation dosimetry.